Protection Relays and Controls Overview

Littelfuse products help protect electrical equipment used in marine, mining, petrochem and general industrial applications. We offer Littelfuse Selco generator protection, controls and alarm panels as well as Littelfuse Startco protection relays and custom power centers.

For decades, we have helped OEMs, electrical installers, design engineers and end-users select the right product for their applications. Today, Littelfuse offers a broader range of products addressing protection and control needs while still providing the same great service and support that customers have learned to expect.

Ground-Fault Protection

Ground faults, also referred to as earth faults, represent the vast majority of electrical faults experienced in most industrial facilities. Ground faults are caused by unintentional contact between an energized phase conductor and ground or equipment frame. The return path of the fault current is through the grounding system and any personnel or equipment that becomes part of that system. Ground faults are frequently the result of insulation breakdown, but can also be caused by other forms of cable damage or human error. It is important to note that damp, wet, and dusty environments require extra diligence in design and maintenance. Since water is conductive, it exposes degradation of insulation and increases the potential for electrical hazards to develop. In fact, studies have indicated that ground faults make up more than 95% of the recorded electrical faults, such as arc flash incidents.

Ground fault protection relays, Ground fault protection relays are designed to detect phase to ground fault on a electrical system and trip when the electrical current exceeds the trip time setting. By quickly detecting the ground fault and initiating the appropriate response, ground fault relays improve electrical safety for workers and minimize damage to equipment due to electrical faults without affecting the uptime of critical operations.

Ground faults are the most common type of fault in an electrical system, and most electrical codes such as the National Electric Code (NEC®) require ground fault protection for industrial systems. POWR-GARD® ground-fault relays are uniquely suited for use on systems with significant harmonic content, with microprocessor-based DFT-filtering technology. Selectable DFT filtering and peak detection algorithms are available to allow excellent filtering for both fixed-frequency and variable- frequency applications, providing sensitive ground fault protection without false tripping. By being able to detect electrical problems in the early stages, ground fault relays can significantly reduce damage and speed up the repair process. Sensitive ground fault relays with advanced filtering capabilities will detect the breakdown in insulation caused by moisture, vibration, chemicals, and dust. Ground fault relays are commonly used in industrial and manufacturing facilities on generators, transformers, switchgear, motor control centers (MCC), panel boards, variable frequency motor drives , welders and heating cables. POWR-GARD ground-fault relays can be surface and DIN-rail mounted, or panel mounted with available adapters. When replacing other ground-fault relays, existing current transformers (CTs) can be used in many cases, greatly simplifying the installation. Adapter plates are also available for many retrofits, minimizing the amount of work required to complete the upgrade.

Resistance Grounding

Resistance Grounding solves the problems commonly associated with both ungrounded systems and solidly grounded systems. Resistance grounding protects a system against transient overvoltages caused by arcing ground faults and it provides a method to locate ground faults. The name is derived from the addition of a resistor between the system neutral and ground, also called neutral grounding resistor or NGR. The specifications of the resistor are user determined to achieve a desired ground-fault current, which must be greater than the system capacitive charging current. For systems 2.4 kV and higher, low-resistance grounding systems can be used. Typically in those systems the ground-fault current is 25 A or above and is cleared within 10 s.

Resistance grounding eliminates excessive ground-fault damage and single phase Arc-Flash Hazards associated with solidly grounded systems by reducing the ground-fault current to 5 A. Per IEEE Standard 141-1993, Arc-flash hazards are eliminated if the ground-fault current is reduced to 5 A or less.

Properly sized resistance grounding systems solve two problems of ungrounded systems—transient overvoltages and difficulty locating ground faults. Resistance grounding systems eliminate transient overvoltages, single phase Arc-Flash hazards, and provide an ability to locate the ground fault. These capabilities reduce unscheduled shutdowns due to electrical faults and equipment damage. The PGN Family of Resistance Grounding Systems include all necessary components to convert or design a resistance- grounded system. Additional ground-fault relays (PGR-4704) can be installed on feeders to provide selective coordination as well as the ability to locate ground faults.

The Littelfuse POWR-GARD resistance grounding line includes the PGN-1000 Low Resistance Grounding System, PGN-3000 High Resistance Grounding System, PGN-5330 Resistance Grounded Relay and the PGM-8325 Neutral Grounding Monitor. Littelfuse POWR-GARD also offers a variety of required and optional accessories such as the PGC Series Current Transformers, PGE Series Sensing Resistors and PGB Series Remote Indication Assemblies, Terminations and Adapters.

Monitoring

Supplemental monitors are single function devices that only look at one abnormal condition and either alarm or provide a means to remove electric power. Visual indication can also be used. The purpose of a monitor is to provide an efficient solution to a dedicated problem. Monitors work together with existing protection, such as fuses, circuit breakers, or protection relays to enhance electrical system safety and performance by monitoring its components. The Littelfuse POWR-GARD monitors are designed for application specific functionality such as insulation monitoring, ground continuity and resistor monitoring.

Ground-check monitors are used to detect problems in equipment ground conductors. Mobile equipment typically has an extra electric wire, sometimes called a pilot wire, routed with the phase and ground conductors. A ground check monitor uses this pilot wire to send a signal down to the equipment to a unique terminating device. The signal then returns on the equipment ground conductor to the monitor. The monitor continuously monitors this loop for open or short circuits, indicating that a problem has occurred.

Insulation monitoring addresses the single most common reason for electrical system failure - insulation breakdown. Insulation monitors can be installed at any point in the system to detect a problem with the insulation. The monitor is connected to one phase and injects a dc signal to continuously measure the system’s insulation resistance. The monitor is typically installed on de-energized feeders or motors and is cycled with feeder’s circuit breaker or motor starter. When the circuit breaker is open, the monitor is energized and begins to monitor the de-energized cables and motor windings. In ungrounded systems, the monitor will continuously monitor the insulation resistance to ground regardless whether the system is energized or de-energized.

Resistor monitoring are designed to detect a failure in the neutral to ground path, which can lead to electrical hazards electrical hazards. Some examples of failure are stolen wires, loose connections, corrosion and broken resistor elements. The resistor monitor continuously monitors the path from system neutral to ground for a problem. When a problem occurs, the NGR monitor provides an alarm.

The Littelfuse POWR-GARD supplemental monitor line includes the PGM-8134 Ground Continuity Monitor, PGM-8325 Neutral Grounding Monitor and PGR-8600 Insulation Monitor. Littelfuse POWR-GARD also offers a variety of required and optional accessories such as the PGC Series Current Transformers, PGE Series Sensing Resistors and PGB Series Remote Indication Assemblies, Terminations and Adapters.

Motor Protection

Motor Protection Relays prevent expensive damage to motors caused by overload and overtemperature, overcurrent, jams and undercurrent, high resistance winding faults, current and voltage unbalance, phase loss, phase reverse, heat from non-electric sources, heavy start-ups, motor jogging or excessive operational cycles. Features, such as integrated protection, metering, data logging, and remote communications extend motor life and maximize process efficiency. Overload protection is required by various electrical codes such as the National Electric Code (NEC®) to reduce the chance of electrical hazards and fire caused by problems with the motor or load. Littelfuse Motor and Feeder Protection relays have a reduced-overcurrent feature that can reduce arc flash hazards during maintenance near energized equipment, allowing for a much safer electrical system.

Motor Protection Relays provide basic overload protection for small motors to advanced protection for large motors to help extend the life of the motor. This is extremely important for large or critical motors or for smaller motors located in hard to access locations. POWR-GARD’s motor protection relays can provide a warning that a problem is developing before damage occurs, as well as uncover potential problems with the customer’s process. Since motors and other electrical equipment represent a significant investment to many industrial operations, motor protection relays are used to extend the life of motors, pumps and drives and improve safety to personnel exposed to the equipment. Motor Protection relays also reduce unscheduled downtime and loss of productivity by continuously monitoring the motor performance to safeguard against unwanted damages.

Motor protection relays are frequently used to protect motors, switchgear, motor control centers (MCC), Variable Frequency Drives and Pumps. The Littelfuse POWR-GARD motor protection relay line includes the PGR-6100 Motor Ground Fault & Insulation Relay, PGR-6200 Motor Protection Relay and PGR-6300 Motor Protection System. Littelfuse POWR-GARD also offers a variety of required and optional accessories such as the PGC Series Current Transformers, PGA Series Current Input Modules, PGW Series and VPG Series Software and PGK Series Panel Mount Adapters for retrofit applications.

Feeder protection relays are designed to detect faults in an electrical distribution system, extend the life of equipment and improve safety to personnel exposed to such equipment. They provide a high degree of flexibility and can coordinate with other protection devices on the system. Feeder protection relays are used in processing, manufacturing, petroleum, chemical, mining, forestry, water, and waste water facilities. Modern Feeder Protection relays are an excellent choice for retrofitting obsolete electromechanical relays.

The Littelfuse POWR-GARD feeder protection relay line includes the PGR-7200 Feeder Protection Relay. Littelfuse POWR-GARD also offers a variety of required and optional accessories such as the PGC Series Current Transformers, PGA Series Current Input Modules and PGK Series Panel Mount Adapters for retrofit applications.